Security and alarm systems are known. A security system may be used to secure a perimeter or an object against theft, tampering, vandalism, invasion, unauthorized use or access, and other kinds of trespass. The secured object or perimeter may be, for example, a vehicle or a building, protected by sensors capable of detecting glass-break events; proximity or movement of a person; openings of doors, trunk, or hood; and other potential breaches of security. A typical security system designed for automotive applications is capable of responding to breaches of security, for example, by activating an alarm and rendering engine starter and engine computer systems inoperative. In addition, some security systems can control various safety and convenience features, such as power door locks, power windows, and entertainment system installed in the vehicle.
Many automotive security systems include a small hand-held remote control device, such as a key-fob, that allows the system's user to perform various operations remotely. For example, the remote control device may lock and disarm the security system, lock and unlock doors and trunk, sound siren, start engine, and perform other functions when corresponding commands are entered by the user. If the security system is configured so that the remote control device can be used to lock and unlock doors of an automobile, the system effectively becomes a keyless entry device, in addition to performing other functions.
It is known in the art to automate the keyless entry function of a remote control device. For example, a hand-held remote control device may be configured to transmit periodically a command that opens doors and possibly also disarms the security system. It may also be the base station that periodically transmits a “feeler” or interrogatory transmission to the hand-held remote control device. When the remote control device receives the interrogatory transmission, it sends a responsive transmission to the base station. The base station and the hand-held device then perform a handshake protocol to verify each other's identity. After the handshake, the hand-held unit may transmit a command directing the base station to perform some function automatically, for example, to unlock one or more doors of an automobile. The doors then automatically unlock when the user carrying the hand-held device approaches the automobile. The feature of automatically unlocking doors when a user approaches the automobile is known as “passive” remote keyless entry. The system is passive in the sense that it opens doors and disarms itself without any deliberate user action, other than approaching the automobile.
A related feature of modern automobile security systems is the ability to automatically lock the doors after a user has exited the vehicle. This feature is known as “passive” locking. Passive locking allows a vehicle to be protected from unauthorized entry into the vehicle even if the user forgets to lock the security system. In some security systems, passive locking can occur after a predetermined time period after the user has exited the vehicle, such as 30 seconds. While passive locking provides great benefit to automotive security systems, a security system containing passive locking presents the possibility that if a vehicle owner's remote control is left inside a vehicle and the user exits the vehicle, the security system can passively lock the vehicle and lock the remote control inside the vehicle. This scenario can cause great inconvenience and cost, not to mention frustration, to the user. Therefore, it would be advantageous to provide a security system that can avoid this inconvenient scenario while still providing the benefits of passive locking.